I've replicated the way ActiveModel generates attributes methods in a module, for fields. This allows you to override a field method and still use super to go up the chain. It removes the need for any alias_method_chain action.

Also corrected the way you have used ActiveSupport::Concern. If other developers need to extend the mongoid api for one-off use or a plugin, then this change makes it easier. It allows a developer to just include a new module into Mongoid::Document and it will preserve the inheritance chain, putting the developer's module first.

Great work on Mongoid btw.